chapter6nutritionandmetabolism-資料下載頁
2025-09-25 22:36本頁面
【正文】 n = number of generation G = t log2 / log Nt – log No Chemostat used for continuous cultures. Rate of growth can be controlled either by controlling the rate at which new medium enters the growth chamber or by limiting a required growth factor in the medium. Continuous culture of microanisms Chemostat Bacteria grow over a range of temperatures。 they do not reproduce below the minimum growth temperattire nor above the maximum growth temperature. Within the temperature growth range there is an optimum growth temperature at which bacterial reproduction is fastest. Effect of temperature on bacterial growth rate Enzymes exhibit a Q10 so that within a suitable temperature range the rate of enzyme activity doubles for every 1039。 C rise in temperature. Microanisms are classified as psychrophiles, , and extremethemophiles based on their optimal growth temperature. Effect of oxygen concentration – reduction potential Effect of oxygen concentration on the growth of various bacteria in tubes of solid medium (a) Obligate aerobesgrowth occurs only in the short distance to which the oxygen diffuses into the medium. (b) Facultative anaerobes growth is best near the surface, where oxygen is available, but occurs throughout the tube. (c) Obligate anaerobesoxygen is toxic, and there is no growth near the surface. (d) Aerotolerant anaerobesgrowth occurs evenly throughout the tube but is not better at the surface because the anisms do not use oxygen. (e) Microaerophiles, aerobic anisms that do not tolerate atmospheric concentrations of oxygengrowth occurs only in a narrow band of optimal oxygen concentration. Effect of pH value on microbial growth Bacteria: Neutral condition Fungi: Acidic condition Actinomycetes: Alkaline condition Water activity The water activity of a solution is 1/100 the relative humidity of the solution (when expressed as a percent), or it is equivalent to the ratio of the solution39。s vapor pressure to that of pure water. aw = P solution / P water Approximate lower aw limits for microbial growth: – for most bacteria, most algae and some fungi as Basidiomycetes,Mucor, Rhizopus. for Halobacterium, Aspergillus… for some saccharomyces species If the concentration of solutes, such as sodium chloride, is higher in the surrounding medium (hypertonic), then water tends to leave the cell. The cell membrane shrinks away from the cell wall (an action called plasmolysis), and cell growth is inhibited. Plasmolysis Normal cell Plasmolyzed cell Control of microbial growth Definitions: Sterilization – the process of destroying all forms of microbial life on an object or in a material. Disinfection – the process of destroying vegetative pathogens but not necessary endospores. Antisepsis – chemical disinfection of skin, mucous membranes or other living tissues
規(guī)章制度相關推薦
鄂ICP備17016276號-1